Fix batch upload usage

When:

• Doing a batch upload,
• Then creating a document using the path endpoint referencing that batch upload id, ex:

POST https://demo.nuxeo.com/nuxeo/api/v1/path/default-domain

{
"entity-type":"document",
"repository":"default",
"type": "File",
"name": "ProjectFrontPage",
"properties":{
	"dc:title":"Project Front Page",
	"file:content":{"upload-batch":"mybatchid","upload-fileId":"0"}
	}
}

Server returns an error 500 saying:
"entity-type": "exception",
"code": "org.nuxeo.ecm.core.api.model.PropertyNotFoundException",
"status": 500,
"message": "Property not found: content"

The same call works fine on nightly.nuxeo.com or a local server.